1. Technical Field
This invention relates to vehicle suspension systems for mounting ground-engaging wheels to a vehicle frame, and, more particularly, to vehicle suspensions having an improved system for mounting a wheel-carrying axle without weakening the axle. In another of its aspects, the invention relates to a trailing arm suspension wherein an axle is mounted to the trailing arm for articulation with respect to the trailing arm.
2. Description of Related Art
The U.S. Pat. No. 3,547,215 to Bird (issued Dec. 15, 1970), discloses a trailing arm suspension wherein a square axle is typically welded to a bracket which is, in turn, secured to the trailing arm of the vehicle suspension structure. The weld securing the axle to the bracket is usually made at the mid-point of the side of the axle where vertical bending moment stresses are neutral. However, these areas are areas of high torsional loading which results from brake torque, vehicle roll and diagonal axle (wheel) walk. The welding at the mid-point of the axle may introduce a point of weakness where cracks can initiate. The weakness in the typical axle welded to a bracket is caused, in part, by the undesirable heat-treating effects and microscopic cracking caused by the welding process upon the axle structure in the localized area adjacent to the weld. In addition, craters or strike marks may form points at which cracks may initiate or at which stresses may become concentrated.
Axles are typically welded to the brackets in order to securely attach the axle to the bracket under this high loading condition. The axle is welded to the axle bracket by a line weld on either side of the bracket. Because it is a line weld, the weld has xe2x80x9cendsxe2x80x9d at which stresses are concentrated and at which cracks may initiate.
A solution to this weld problem is disclosed in U.S. Pat. No. 4,693,486 to Pierce et al. (issued Sep. 15, 1987), which discloses a trailing arm suspension in which an axle secured to a trailing arm by a wrapper plate partially surrounding the axle, a bolt compresses the wrapper plate about the axle so that the wrapper plate supports and strengthens the axle, and a circular plug weld is positioned on the axle in a circular opening in the wrapper plate to attach the wrapper plate to the axle. Although this system is a significant improvement over the previous welds to the axle, the plug weld still may be a source of stress cracks in the axle.
The U.S. Pat. No. 5,116,075 to Pierce (issued May 26, 1992), discloses a trailing arm suspension wherein a wrapper plate is mounted to an axle through mechanical compression and without welding to the axle. Adapter plates mounted to the ends of the plate apply a compressive force to the corners of a square axle when the wrapper plate is compressed against the axle by a bolt. The wrapper plate is mounted on a pair of side plates which in turn are fixed to the trailing arm. Although the suspension is effective to overcome the potential of crack initiation of the axle between the axle and the axle bracket, the wrapper plate is relatively heavy and a considerable amount of skilled labor is involved in assembling the axle to the trailing arm suspension, frequently at the point of assembly to the axle and suspension to the vehicle. The forces of compression tend to be somewhat uneven. The compressive forces exerted by the adapter plates in particular can be relatively high compared to the compressive forces exerted by the wrapper plate.
The U.S. patent to Kaufman, U.S. Pat. No. 5,328,159, discloses a trailing arm suspension in which a pair of U-shaped bracket plates mount U-shaped rubber pads and are clamped onto a square axle with the rubber pads between the bracket plates and the axle. The axle is at a slight angle with respect to the bracket plates so that the bracket plates present a slight diagonal force to the side walls of the axle. The axle is presumably welded to the bracket plates.
The U.S. patent to Dilling et al., U.S. Pat. No. 5,366,237, discloses a trailing arm suspension in which a pair of semi-cylindrical bracket plates are welded to a round axle through an opening between the two plates and along the parting lines between the bracket plates. The axle extends through two openings in the trailing arm and is secured thereto by welding the bracket plates to the beams. The bracket plates are relatively wide and do not deflect when the axle bends. Thus, stress risers can form on the axle at the side edges of the bracket plates. A brake actuator is mounted to the trailing arms for operating brakes on the axle wheels. Welding to the axle can also introduce undesirable microscopic cracks which can initiate fatigue cracks and ultimately lead to failure of the axle due to torsional stress on the axle.
It is also common to mount a track bar between a trailing arm and a central portion of an axle. The track bar is mounted to the axle through a tower bracket which is welded to a central portion of the axle. The welds between the tower bracket and the axle can introduce in the axle weak points and microscopic cracks which can form sources of cracks which may ultimately result in failure of the axle under severe or prolonged loading conditions.
DE 42 32 779 and DE 42 32 778 disclose a vehicle suspension system with an air spring or a leaf spring wherein a relatively square axle is tied in to the suspension through a U-bolt and axle plate which bears against the axle at an upper portion. A filler can be provided in the bottom of the U-bolt. A ring received in an opening in the axle plate is welded to an upper surface of the axle. Frictional force resulting from pressure applied by the axle plate at the upper corners of the axle and by the filler plate at the bottom corners of the axle coupled with the welded ring is said to hold the axle against movement in the mounting. A U-bolt does not give consistent and sufficient compressive forces to adequately prevent slippage of an axle in the mounting and does not work well with round axles.
In accordance with the invention, a trailing arm suspension for mounting ground-engaging wheels to a vehicle frame has an axle mounted to a trailing arm through an axle-beam connector. The suspension comprising at least two arms adapted to be secured to opposite sides of the frame and at least one wheel-carrying axle mounted to the arms through an axle-mounting assembly. Each of the axle-mounting assemblies comprises at least one beam-axle connector which is mounted to one of the arms at one end thereof through a bushed connection and is connected to the axle at another end thereof. Each of the arms forms a collar which receives the axle. An elastomeric layer is positioned between the axle and the collar for articulation between the axle and the collar. Preferably, the beam-axle connector is rigidly mounted to the axle at the other end thereof.
In a preferred embodiment of the invention, there are two beam-axle connectors, one on each side of each arm, and each beam-axle connector is connected to the arm and to the axle in the same manner. Further, each of the beam-axle connectors is identical and is symmetrical about a longitudinal axis. Each beam-axle connector is generally triangular in two dimensional configuration and has a reinforcing gusset at an upper portion thereof and at a lower portion thereof. Preferably, each beam-axle connector further includes an arcuate plate at the other end thereof and through which the beam-axle connector is mounted to the axle.
In one embodiment, the beam-axle connector is mounted to the axle through a hollow wrapper band which circumscribes the axle and is under tension sufficient to compress the axle at at least two sets of diametrically opposed and circumferentially spaced external surfaces of the axle and to prevent movement of the axle with respect to the wrapper band under ordinary service conditions. To this end, the arcuate plate extends about 180xc2x0 around the axle and mates with a second arcuate plate to form a hollow wrapper band which circumscribes the axle and is under tension sufficient to compress the axle at at least two sets of diametrically opposed and circumferentially spaced external surfaces of the axle and to prevent movement of the axle with respect to the wrapper band under ordinary service conditions.
The invention provides for an assembly of an axle to a suspension, preferably a trailing arm suspension, whereby the axle is maintained in a high state of compression essentially sufficient to couple the axle to the axle mounting without any welding between the axle and the wrapper band. The axle is thus stronger because it is not welded to the mounting assembly. However, the axle is maintained in position on the mounting assembly and thus in a fixed position on the trailing arm suspension by frictional forces created by the compression between the mounting assembly and the axle. The axle mounting is stronger than previous system and further is adaptable to automated assembly techniques. Thus, the axle mounting assembly is less expensive to assemble, more reliable in service, longer lived and lower in weight compared to similar strength axle mounting assemblies.